The invention relates to a probe, and more particularly, to a probe for making temperature measurements of a semiconductor substrate.
Many semiconductor device manufacturing processes require a tight control of temperatures associated with a semiconductor wafer or substrate during processing to increase device performance and yield as well as to ensure process repeatability. In certain processes, if temperature differentials in the wafer rise above 1-2.degree. C./cm at 1200.degree. C., the resulting stress may cause slips in silicon crystals and may destroy potential semiconductor structures on the wafer. To avoid damage to the substrate and undesirable process variations, a precise temperature monitoring device for the substrate is needed.
One method for determining substrate temperature applies the principles of pyrometry. Pyrometers, or devices based on pyrometry, exploit the general property that objects emit radiation with a particular spectral content and intensity that is characteristic of their temperature. By measuring the emitted radiation, the object's temperature can be determined. In systems that incorporate pyrometers, a thermal reflector is positioned near the substrate to create a virtual black body cavity between the reflector and the substrate. Additionally, a temperature probe with a light pipe is used to sample radiation in the cavity through an aperture in the reflector. The sampled intensity is passed through an optical transmitter to the pyrometer where it is converted to temperature information. Further, to increase the precision of the temperature monitoring process, the emitted radiation intensity can be monitored via a plurality of temperature probes and pyrometers which monitor the localized regions of the substrate and perform appropriate conversions to obtain temperature. Temperature readings from various probes and pyrometers can be used for real-time control of heating elements in the rapid thermal processing (RTP) of substrates.
Conventional temperature probes typically use sapphire light pipes that pass through conduits which extend from the backside of a base of a process chamber through the top of a reflector. Although expensive, sapphire light pipes have relatively small scattering coefficients and tend to have greater transverse light rejection. These capabilities provide more accurate and localized measurements. Additionally, as sapphire is inert, light pipes made of sapphire do not suffer out-gassing problems. However, as sapphire light pipes are small (about 0.125 inch in diameter), they are relatively fragile components that can be easily chipped during handling. Chipped sapphire light pipes transmit less light to the pyrometers, resulting in inaccurate temperature readings which can adversely impact the operations of the processing equipment.
As costs associated with replacing chipped probes can quickly become a significant portion of the operating expenses, a durable, cost-effective temperature probe that can operate in a high temperature processing chamber is needed.